This is a controlled trial designed to determine short- and long-term effects of repeated tDCS on the P300 component of event-related evoked potentials in patients with chronic neuropathic pain due to Complex regional Pain Syndrome (CRPS) or diabetic neuropathy as compared with healthy subjects.

Further study details as provided by Soroka University Medical Center:

Primary Outcome Measures:

Changes in the amplitude of P300 [ Time Frame: 15 min after and 120 min after the 1st tDCS, 15 min after and 120 min after the 5st tDCS, and at the follow up 1 week after the 5th tDCS. ] [ Designated as safety issue: No ]

Changes in the Latency of P300 [ Time Frame: 15 min after and 120 min after the 1st tDCS, 15 min after and 120 min after the 5st tDCS, and at the follow up 1 week after the 5th tDCS. ] [ Designated as safety issue: No ]

Secondary Outcome Measures:

Changes in Pain Intensity-will be calculated as the difference in scores on the 11-point numerical pain rating scale (0-10) [ Time Frame: 15 min after and 120 min after each tDCS stimulation ] [ Designated as safety issue: No ]

Changes in Pain Thresholds for Tactile and Thermal Stimuli will be calculated as the difference between ratings obtained form pain threshold measurements before- and after tDCS [ Time Frame: 15 min after and 120 min after each tDCS stimulation ] [ Designated as safety issue: No ]

The latency and amplitude of P300, subjective pain intensity, and pain thresholds for tactile and thermal stimuli will be determined at before and 15 min and 120 min after the 1st and 5th tDCS/sham procedure, To receive tDCS/sham treatment, two electrodes will be placed on the patient´s skull (for details see section Methods) and the patient will rest for 5 min. After that, the patient will receive 20 minutes of 2 mA tDCS/sham. Subjective pain intensity, and pain thresholds for tactile and thermal stimuli will be determined before-, 15 min after and 120 min after each tDCS/Sham procedure. At the 1st and 5th tDCS/Sham session, the latency and amplitude of P300 will be determined before-, 15 min after and 120 min after the tDCS/sham procedure.

Experimental: 2-DN

20 tDCS naïve patients with diabetic neuropathy

Device: TDCS/sham procedure on five consecutive days

The latency and amplitude of P300, subjective pain intensity, and pain thresholds for tactile and thermal stimuli will be determined at before and 15 min and 120 min after the 1st and 5th tDCS/sham procedure, To receive tDCS/sham treatment, two electrodes will be placed on the patient´s skull (for details see section Methods) and the patient will rest for 5 min. After that, the patient will receive 20 minutes of 2 mA tDCS/sham. Subjective pain intensity, and pain thresholds for tactile and thermal stimuli will be determined before-, 15 min after and 120 min after each tDCS/Sham procedure. At the 1st and 5th tDCS/Sham session, the latency and amplitude of P300 will be determined before-, 15 min after and 120 min after the tDCS/sham procedure.

Experimental: 3-RPNP

20 tDCS naïve patients with resistant peripheral neuropathic pain

Device: TDCS/sham procedure on five consecutive days

The latency and amplitude of P300, subjective pain intensity, and pain thresholds for tactile and thermal stimuli will be determined at before and 15 min and 120 min after the 1st and 5th tDCS/sham procedure, To receive tDCS/sham treatment, two electrodes will be placed on the patient´s skull (for details see section Methods) and the patient will rest for 5 min. After that, the patient will receive 20 minutes of 2 mA tDCS/sham. Subjective pain intensity, and pain thresholds for tactile and thermal stimuli will be determined before-, 15 min after and 120 min after each tDCS/Sham procedure. At the 1st and 5th tDCS/Sham session, the latency and amplitude of P300 will be determined before-, 15 min after and 120 min after the tDCS/sham procedure.

The latency and amplitude of P300, subjective pain intensity, and pain thresholds for tactile and thermal stimuli will be determined at before and 15 min and 120 min after the 1st and 5th tDCS/sham procedure, To receive tDCS/sham treatment, two electrodes will be placed on the patient´s skull (for details see section Methods) and the patient will rest for 5 min. After that, the patient will receive 20 minutes of 2 mA tDCS/sham. Subjective pain intensity, and pain thresholds for tactile and thermal stimuli will be determined before-, 15 min after and 120 min after each tDCS/Sham procedure. At the 1st and 5th tDCS/Sham session, the latency and amplitude of P300 will be determined before-, 15 min after and 120 min after the tDCS/sham procedure.

Have not responded to at least two medications of the following groups: Opioids. Tricyclics, SSRI, SNRI, Pregabalin, Gabapentin, Anticonvulsants.

Positive LANSS or CRPS criteria as follows:

Continuing pain which is disproportionate to any inciting event or for CRPS diagnosis.

Must report at least one symptom (symptoms here are reports by subject) in each of the four following categories: sensory, vasomotor, sudomotor/edema, motor/trophic.

Must display at least one sign (signs here refer to objective observation/testing) in in each of the four following categories: sensory, vasomotor, sudomotor/edema, motor/trophic;

Must meet resistant neuropathic pain criteria - pain that is neuropathic in characters that at least two neuropathic medications not from the same group have been tried for at least a month without improvement or severe side-effects were experienced. Resistant neuropathic pain with a score for "average pain in the last 24 hours" ≥4 on a numeric scale 0-10

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Please refer to this study by its ClinicalTrials.gov identifier: NCT00815932